July 17, 2008
PASADENA, Calif. -- NASA's Deep Impact spacecraft has created a video of
the moon transiting (passing in front of) Earth as seen from the spacecraft's
point of view 50 million kilometers (31 million miles) away. Scientists are
using the video to develop techniques to study alien worlds.
"Making a video of Earth from so far away helps the search for other life-bearing
planets in the Universe by giving insights into how a distant, Earth-like alien
world would appear to us," said University of Maryland astronomer Michael A'Hearn,
principal investigator for the Deep Impact extended mission, called Epoxi.
Deep Impact made history when the mission team directed an impactor from the
spacecraft into comet Tempel 1 on July 4, 2005. NASA recently extended the mission,
redirecting the spacecraft for a flyby of comet Hartley 2 on Nov. 4, 2010.
Epoxi is a combination of the names for the two extended mission components:
a search for alien (extrasolar) planets during the cruise to Hartley 2, called
Extrasolar Planet Observations and Characterization (EPOCh), and the flyby of
comet Hartley 2, called the Deep Impact eXtended Investigation (DIXI).
During a full Earth rotation, images obtained by Deep Impact at a 15-minute
cadence have been combined to make a color video. During the video, the moon
enters the frame (because of its orbital motion) and transits Earth, then leaves
the frame. Other spacecraft have imaged Earth and the moon from space, but Deep
Impact is the first to show a transit of Earth with enough detail to see large
craters on the moon and oceans and continents on Earth.
"To image Earth in a similar fashion, an alien civilization would need technology
far beyond what Earthlings can even dream of building," said Sara Seager, a planetary
theorist at the Massachusetts Institute of Technology, Cambridge, Mass., and a
co-investigator on Epoxi. "Nevertheless, planet-characterizing space telescopes
under study by NASA would be able to observe an Earth twin as a single point of
light -- a point whose total brightness changes with time as different land masses
and oceans rotate in and out of view. The video will help us connect a varying point
of planetary light with underlying oceans, continents, and clouds -- and finding
oceans on extrasolar planets means identifying potentially habitable worlds." said Seager.
"Our video shows some specific features that are important for observations of
Earth-like planets orbiting other stars," said Drake Deming of NASA's Goddard Space
Flight Center in Greenbelt, Md. Deming is deputy principal investigator for Epoxi,
and leads the EPOCh observations. "A 'sun glint' can be seen in the movie, caused by
light reflected from Earth's oceans, and similar glints to be observed from extrasolar
planets could indicate alien oceans. Also, we used infrared light instead of the
normal red light to make the color composite images, and that makes the land masses
much more visible." That happens because plants reflect more strongly in the near-infrared,
Deming explained. Hence the video illustrates the potential for detecting vegetated
land masses on extrasolar planets by looking for variations in the intensity of their
near-infrared light as the planet rotates.
The University of Maryland is the Principal Investigator institution,
leading the overall Epoxi mission, including the flyby of comet
Hartley 2. NASA Goddard leads the extrasolar planet observations.
NASA's Jet Propulsion Laboratory, Pasadena, Calif., manages Epoxi for
NASA's Science Mission Directorate, Washington. The spacecraft was
built for NASA by Ball Aerospace & Technologies Corp., Boulder, Colo.
To see the video, visit:
http://www.nasa.gov/topics/solarsystem/features/Epoxi_transit.html
Media contacts: DC Agle 818-393-9011
Jet Propulsion Laboratory, Pasadena, Calif.
agle@jpl.nasa.gov
Nancy Neal-Jones / Bill Steigerwald 301-286 0039 / 5017
NASA Goddard Space Flight Center, Greenbelt, Md.
Nancy.N.Jones@nasa.gov / william.a.steigerwald@nasa.gov
Lee Tune 301-405-4679
University of Maryland, College Park
ltune@umd.edu
David L. Chandler 617-253-2704
Massachusetts Institute of Technology, Cambridge, Mass.
dlc1@MIT.EDU
2008-137